JP2019527937A - Use of an electric field to peel a piezoelectric layer from a donor substrate - Google Patents

Abstract

The present invention relates to a method for transferring a piezoelectric layer onto a support substrate. The invention also relates to a stripping chamber for performing at least part of the method. The method of the present invention for peeling a piezoelectric layer from a donor substrate on a support substrate comprises: a) providing a predetermined segmented region in the piezoelectric donor substrate; and b) attaching the piezoelectric donor substrate to the support substrate to form a composite. And c) peeling the piezoelectric layer from the piezoelectric donor substrate comprising applying an electric field. By using an electric field, the peeling step can be performed at a lower temperature compared to the prior art. [Selection] Figure 2

Description

  The present invention relates to a method for transferring a piezoelectric layer onto a support substrate. The invention also relates to a stripping chamber for performing at least part of the method.

  There is a growing interest in composite structures comprising a support substrate such as silicon or sapphire with a thin piezoelectric layer attached. In order to obtain such a composite structure, it has been proposed to use a SmartCut (TM) type process known from silicon on insulator substrates.

  This process can utilize a piezoelectric donor substrate having a predetermined segmented region inside the donor substrate. The predetermined divided region can be obtained by implanting ions into the donor substrate. Thereafter, the donor substrate is attached to the support substrate and subjected to a heat treatment to strengthen the bond between the donor and the support substrate and to peel off the remaining portion of the donor substrate in a predetermined segmented region, thereby The layer of the piezoelectric donor substrate is transferred onto the support substrate.

  Under the influence of the higher temperature during heat treatment, the default generated by the implanted ions in a given split region grows, resulting in local strain, which results in delamination at a given heat balance, and so on. Layer transfer onto the support substrate.

  However, in the case of a piezoelectric donor substrate, it is difficult to transfer without damaging the layer. This is due to a large difference in coefficient of thermal expansion (CTE mismatch) between the piezoelectric donor substrate and the support substrate. Therefore, a strain appears at the interface between the donor and the supporting substrate during the heat treatment, and this strain is suddenly relaxed at the moment of peeling, leading to damage of the transferred layer.

  Accordingly, it is an object of the present invention to provide an alternative layer transfer method that is particularly important for reducing the failure of the transferred piezoelectric layer due to CTE mismatch.

  This object is achieved by a method for transferring a piezoelectric layer onto a support substrate according to the present invention, the method comprising: a) providing a predetermined divided region in the piezoelectric donor substrate; and b) the piezoelectric donor substrate on the support substrate. Attaching to form a composite; and c) peeling the piezoelectric layer from the piezoelectric donor substrate comprising applying an electric field. By applying an electric field, the electric field causes deformation in the piezoelectric donor substrate, which further weakens the default region of a given split region due to the construction of complementary strains, so that the piezoelectric properties of the donor substrate To weaken a predetermined segmented area. As a result, it is possible to reduce the heat balance necessary for completely peeling the peeled piezoelectric layer.

  According to certain embodiments, the piezoelectric donor substrate may be made from a single piezoelectric material, a so-called bulk piezoelectric substrate. According to other embodiments, the piezoelectric donor substrate may be made from a layer of piezoelectric material provided on a handle substrate. In the second case, a handle substrate having a CTE similar to that of the support substrate can be selected. A CTE difference between the handle substrate and the support substrate of less than 10% is greater for the larger of the two CTEs compared to the larger CTE difference and / or larger than the support substrate. Compared to the use of a bulk piezoelectric substrate with a CTE difference, it is possible to increase the heat balance for the heat treatment supporting the method described above.

  According to an embodiment, the method may further include an ion implantation step for forming a predetermined divided region, and a heat treatment step for the ion-implanted piezoelectric donor substrate, the heat treatment step being performed at 0 ° C. to It can be carried out in the temperature range of 200 ° C. for 1 hour to 24 hours. In the heat treatment step, defects in a predetermined divided region can be grown.

  According to a preferred variant, step b) can comprise a heat treatment at a temperature of up to 100 ° C. or up to 50 ° C., or in one variant can be carried out at a room temperature of 15 ° C. to 25 ° C. In manufacturing processes where delamination is achieved only by heat treatment, it is necessary to stabilize the bonding interface prior to the delamination step to prevent undesirable bonding defects at the moment of delamination. In the prior art, enhanced bonding is obtained by heating the composite prior to peeling. As already mentioned above, such a heat treatment causes problems associated with differences in thermal expansion coefficients in the case of piezoelectric donor substrates. By using an electric field during peeling, the bonding energy between the donor substrate and the support substrate can be lowered compared to the bonding energy required only for thermally induced peeling. This is due to the fact that the influence of mechanical strain due to the presence of the electric field is very limited to the piezoelectric donor substrate and has little influence on the interface with the support substrate.

According to a preferred variant, step b) can be carried out at a pressure of less than 10 ⁻² mbar.

  Step c) can preferably be carried out at temperatures below 100 ° C., more particularly below 50 ° C., even more particularly at room temperature between 15 ° C. and 25 ° C. Thus, exfoliation can be obtained at lower temperatures compared to exfoliation processes that are not assisted by an electric field.

  According to a preferred embodiment, the electric field can be applied using a chuck comprising at least one electrode. By using such a chuck, the electric field can be made available in a simple manner. The chuck may comprise holding means independent of such electrodes, for example implemented by vacuum or electrostatic properties.

  Advantageously, the surface of the composite piezoelectric donor substrate can be placed on a chuck. In this configuration, the process can be performed independently of the electrical characteristics of the support substrate.

  According to one variant, the chuck can comprise a plurality of interdigitated electrodes separated by an electrical insulator, in particular a ceramic. With this shape, it is possible to generate an appropriate electric field using only one electrode. This simplifies the processing chamber design.

  According to one embodiment, the voltage applied to the chuck is up to 10 kV, in particular in the range of 1 kV to 5 kV. In this voltage range, an electric field strong enough to deform the piezoelectric donor substrate is created, so that delamination can occur with a lower heat balance.

  According to one variant, the donor substrate-support substrate complex may be sandwiched between a chuck and in particular a second electrode comprised in the second chuck. In designs that use electrodes on both sides of the composite, the voltage applied to the first and second electrodes can be lower than with only one electrode.

  In this variant of the invention, the voltage applied to the electrostatic chuck can preferably be up to 5 kV, in particular in the range from 200 V to 1 kV.

  According to one embodiment, the electric field lines can be essentially parallel to the polarization direction of the piezoelectric donor substrate. By aligning the electric field with the polarization direction of the piezoelectric donor substrate, the magnitude of the resulting strain can be increased, facilitating the stripping step.

The piezoelectric donor substrate may be one of LiTaO ₃ (LTO), AlN, ZnO, Pb [Zr _x Ti _1-x ] O ₃ (0 ≦ x ≦ 1) (PZT), and LiNbO ₃ (LNO). It is preferable that The support substrate can preferably be a semiconductor substrate, in particular a Si wafer, an insulator, in particular a sapphire wafer, or a metal, in particular a Mo wafer.

  The object of the invention is also achieved by a peeling chamber comprising one or two chucks for applying an electric field to the piezoelectric layer for performing step c) as described above. The stripping chamber can also be used for performing step b), according to one variant. By using the chuck, an electric field that causes deformation of the piezoelectric substrate can be generated, so that a predetermined divided region can be weakened. As a result, the thermal budget required to perform the stripping of the piezoelectric layer from the rest of the donor substrate can be reduced compared to a process that uses only thermal energy for the stripping step. Therefore, the adverse effect of a large difference in thermal expansion coefficient between the donor substrate and the support substrate can be reduced.

  Another object of the present invention is to apply an electric field in order to weaken a predetermined divided area inside the composite, and a holding means for holding the composite, in particular a vacuum and / or electrostatic holding means. For the electrode to achieve. According to one variant, the electrostatic holding means and the electrode for applying the electric field may be independent of each other. In this way, the holding action and the weakening action as described above with respect to the method can be optimized with respect to each other.

  The present invention will be described in more detail below using advantageous exemplary embodiments in conjunction with the accompanying drawings.

It is the schematic which shows embodiment of the method of transferring a piezoelectric layer on a support substrate. It is the schematic which shows embodiment of the method of transferring a piezoelectric layer on a support substrate. It is the schematic which shows embodiment of the method of transferring a piezoelectric layer on a support substrate. It is the schematic which shows embodiment of the method of transferring a piezoelectric layer on a support substrate. It is the schematic which shows embodiment of the method of transferring a piezoelectric layer on a support substrate. It is the schematic which shows the structure by the 2nd Embodiment of this invention. It is the schematic which shows the structure by the 3rd Embodiment of this invention.

  1a to 1e show an embodiment of a method for transferring a piezoelectric layer onto a support substrate.

  In the process step shown in FIG. 1 a corresponding to step a) of the method according to the invention, a predetermined segmented region 1 is produced in the piezoelectric donor substrate 3 by implanting ions 5.

The piezoelectric donor substrate 3 may be, for example, LiTaO ₃ (LTO), AlN, ZnO, Pb [Zr _x Ti _1-x ] O ₃ (0 ≦ x ≦ 1) (PZT), and LiNbO ₃ (LNO). it can. In the following, by way of example only according to the present invention, the piezoelectric donor substrate is a bulk piezoelectric substrate made from LTO. According to a variant, the donor substrate can comprise a handle substrate with a piezoelectric layer on top.

In order to obtain a predetermined divided region 1 inside the piezoelectric donor substrate 3, ions / cm ² of a mixture of H ⁺ or He ⁺ or H ⁺ / He ⁺ of 5 * 10 ¹⁶ to 2 * 10 ¹⁷ Implanted with an energy of about 10 keV to 1 MeV depending on the desired depth d of 1. Under the implantation conditions described above, the depth d is about 60 nm to 6 μm.

  The next step shown in FIG. 1b is a first heat treatment step for growing a defect 7 forming a predetermined divided region 1 generated by ion implantation. The roughness of the surface 9 is less than 5 nm RMS. According to the present invention, this first heat treatment step is performed at a temperature of 0 ° C. to 200 ° C. for about 1 to 24 hours.

  Step b) according to the invention is shown in FIG. This step consists in attaching the piezoelectric donor substrate 3 to the support substrate 11, in particular by bonding, thereby forming a composite 13. The support substrate 11 can be a semiconductor substrate such as a Si wafer, an insulator such as sapphire, or a metal such as Mo.

The joining step is performed under atmospheric pressure or vacuum, typically under a primary vacuum of less than 10 ⁻² mbar, in particular on the order of 10 ⁻³ to 10 ⁻⁴ mbar. In order to strengthen the bond between the two substrates 3 and 11, the bonding is performed at a temperature of up to 100 ° C.

  FIG. 1d shows the next step in the manufacturing process. This step corresponds to step c) according to the invention. An electric field is applied to the composite 13 and the electric field lines 15 are essentially perpendicular to the predetermined segmented region 1. According to one aspect of the present invention, the electric field lines 15 are essentially parallel to the polarization axis 17 (or poling axis) of the piezoelectric donor substrate 3 to optimize the piezoelectric effect. Due to the piezoelectric properties, the presence of the electric field 15 causes a mechanical deformation in the z direction inside the piezoelectric support substrate 3. This deformation further weakens the predetermined divided region 1. In order to obtain the desired electric field, a voltage of up to 10 kV is applied (see further below with respect to FIGS. 2 and 3).

  Depending on the strength of the electric field, complete delamination of the remaining portion 19 of the piezoelectric donor substrate from the modified composite 13 ′ comprising the support substrate 11 and the transferred piezoelectric layer 21 is predetermined as shown in FIG. 1e. Can occur in any of the divided regions.

  According to one variant, delamination as shown in FIG. 1 e can also be obtained by heating the composite 13 during or after application of the electric field 15. In this second heat treatment step, temperatures up to 100 ° C. are used for final stripping. The selection of temperature depends on the conditions of the first heat treatment step and the strength of the electric field 15.

  Using the method according to the invention, the thin piezoelectric layer 21 is transferred onto the support substrate 11 without being disturbed by the existing large differences in the coefficient of thermal expansion between the piezoelectric layer material 21 and the support substrate 11. Is possible.

  The remaining portion 19 of the piezoelectric donor substrate can then be reused as the donor substrate 3 to resume the process as described with respect to FIGS.

  FIG. 2 schematically shows a configuration according to a second embodiment of the present invention. FIG. 2 shows a stripping chamber 31 used to perform at least step c) of the method according to the invention as shown in FIG. 1d.

  The stripping chamber comprises a chuck 33 including a positive electrode 35 and a negative electrode 37 so that an electric field 39 can be applied to the composite 13 including the piezoelectric donor substrate 3 and the support substrate 11 as described in detail with respect to the first embodiment. Is provided. The description of the features of the first embodiment is not repeated again, but is hereby incorporated by reference. The chuck can comprise further means for holding the composite 13, for example vacuum or electrostatic means. In this embodiment, these means are independent from the electrodes 35 and 37.

  The composite 13 is positioned on the chuck 33 such that the piezoelectric donor substrate 3 of the composite 13 is disposed on the chuck 33.

  The positive electrode 35 and the negative electrode 37 are arranged so that the electric field 39 is essentially perpendicular to the surface of the chuck 33 at least within the thickness d ′ of the piezoelectric donor substrate 3. Since the polarization axis 17 of the piezoelectric donor substrate is also perpendicular to the chuck 33, the piezoelectric effect can be optimized, thereby generating mechanical strain in a predetermined divided region 1 and further weakening. Can do.

  According to one variant, it may be the support substrate that is arranged on the chuck 33, especially when the electric field is sufficiently strong. However, for the insulating support substrate 11, the piezoelectric donor substrate 3 is preferably disposed on the chuck 33.

  In one variation, the positive electrode 35 and the negative electrode 37 are interdigitated and an electrical insulator (not shown), eg, a thin ceramic layer, is disposed therebetween.

  The control unit of the divided chamber 31 is configured to be able to apply a voltage of 10 kV at maximum, preferably 1 kV to 5 kV to the electrodes. In the present embodiment, only one electrostatic chuck is required, which simplifies the design of the peeling chamber 31.

  FIG. 3 schematically shows a configuration according to a third embodiment of the present invention. FIG. 3 shows a second embodiment of a stripping chamber 51 used for performing at least step c) of the method according to the invention as shown in FIG. 1d. The description of the features of the first and second embodiments is not repeated again, but is hereby incorporated by reference.

  In this embodiment, two chucks 53 and 55 are used. The lower chuck 53 includes a positive electrode 57, and the upper chuck 55 includes a negative electrode 59. According to one variant, the polarizations can be interchanged with each other. The composite 13 is sandwiched between two chucks 53 and 55.

  Further, in this configuration, the electric field line 61 is parallel to the polarization direction 17 of the piezoelectric donor substrate in order to optimize the piezoelectric effect, resulting in an optimized weakening in the predetermined divided region 1.

  In this electrode configuration, a maximum voltage of 5 kV, in particular 200 V to 1 kV, is applied to the electrodes 53 and 55, and a desired division region 1 is obtained without observing peeling at the interface between the piezoelectric donor substrate 3 and the support substrate 11. An effect can be obtained.

  The stripping chambers 31 and 51 of the second and third embodiments can, according to a further variant, be used for step b) of the method according to the invention to realize the mounting step as shown in FIG. 1c. Furthermore, the stripping chamber can, according to a further variant, comprise heating means and / or a vacuum pump so that heat treatment can be performed and / or process steps under vacuum can be performed.

  The features of any one of the first to third embodiments can be combined individually or in groups with any one of the other embodiments to form further variants of the method and / or the dividing chamber according to the invention. can do.

Claims (18)

A method of transferring a piezoelectric layer onto a support substrate,
a) providing a predetermined segmented region (1) in the piezoelectric donor substrate (3);
b) attaching the piezoelectric donor substrate (3) to a support substrate (11) to form a composite (13);
c) peeling the piezoelectric layer (21) from the piezoelectric donor substrate (3) comprising applying an electric field (15);
Including the method.   The method of claim 1, wherein the piezoelectric donor substrate is made from a bulk piezoelectric substrate.   The method of claim 1, wherein the piezoelectric donor substrate is made from a layer of piezoelectric material provided on a handle substrate.   The process according to any one of claims 1 to 3, wherein step b) comprises a heat treatment at a temperature of at most 100 ° C, in particular at most 50 ° C, or is carried out at room temperature of from 15 ° C to 25 ° C. Step b) is carried out at a pressure of less than ¹⁰ -2 mbar, A method according to any one of claims 1 to 4.   6. A process according to any one of the preceding claims, wherein step c) is performed at a temperature below 100 <0> C, more particularly below 50 <0> C, even more particularly at a room temperature between 15 <0> C and 25 <0> C.   The method according to any of the preceding claims, wherein the electric field (15) is applied using a chuck comprising at least one electrode.   The method of claim 7, wherein a surface of the piezoelectric donor substrate of the composite is disposed on the chuck.   9. Method according to claim 8, wherein the chuck comprises a plurality of interdigitated electrodes separated by an electrical insulator, in particular a ceramic.   The method according to claim 9, wherein the voltage applied to the chuck is at most 10 kV, in particular in the range of 1 kV to 5 kV.   9. A method according to claim 7 or 8, wherein the composite is sandwiched between the chuck and in particular a second electrode contained in a second chuck.   The method according to claim 11, wherein the voltage applied to the electrostatic chuck is at most 5 kV, in particular in the range from 200 V to 1 kV.   The method according to any of the preceding claims, wherein the electric field lines (15) are essentially parallel to the polarization direction (17) of the piezoelectric donor substrate (3). The piezoelectric donor substrate (3) is LiTaO ₃ (LTO), AlN, ZnO, Pb [Zr _x Ti _1-x ] O ₃ (0 ≦ x ≦ 1) (PZT), and LiNbO ₃ (LNO). The method according to claim 1, wherein the method is one.   15. A method according to any one of the preceding claims, wherein the support substrate (11) is a semiconductor substrate, in particular a Si wafer, or an insulator, in particular a sapphire wafer, or a metal, in particular a Mo wafer.   16. Stripping for performing step c) according to any one of the preceding claims, comprising one or two chucks comprising first and / or second electrodes for applying an electric field to the piezoelectric layer. Chamber.   17. A peeling chamber according to claim 16, wherein at least one of the chucks comprises holding means, in particular vacuum and / or electrostatic holding means.   18. A stripping chamber according to claim 17, wherein the first and / or second electrode is independent of the electrostatic holding means.

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